1. Field of the Invention
The present invention relates to a sheet storing apparatus, and more specifically, a sheet storing apparatus wherein sheets ejected from an image forming apparatus such as a copying machine, a laser printer, etc. are stacked in order so that a duplex/composite copying operation or a stapling operation will be available.
2. Description of Related Art
A conventional sheet storing apparatus wherein copied sheets are transported to a sheet storing unit one after another and stacked in order, whether a horizontal storing type or a vertical storing type, still needs to be reformed in order to prevent a sheet jam and a page disorder which may be caused by a collision between a sheet entering the sheet storing unit and sheets already stored therein. Especially, copied sheets are generally heated by a fixing device and accordingly the end portions are curled. Therefore, measures to prevent such problems are so important.
In Japanese Laid Open Patent Publication No. 61-54691, a flexible sheet pressing member for guiding the leading end of a sheet and preventing the sheet from curling up is disclosed. However, the sheet pressing member offers resistance to a traveling sheet, so that designating proper pressure on each of the sheets which vary in thickness and stiffness is difficult. Also, the Publication does not teach anything about measures for the trailing end of a sheet. As measures for the trailing end of a sheet, it is an idea that a surface on which sheets are stacked is disposed more distant from the entrance of the storing unit. However, this arrangement needs a large space, so that it is not preferable. Additionally, in a vertical type of sheet storing unit, sheets are more liable to cover the entrance because of the falling and bending of the sheets.
Japanese Laid Open Patent Publication No. 57-72537 discloses an apparatus having a pressing plate for pressing the leading end of a sheet each time a sheet enters a sheet storing unit. However, in this publication, no measures for the trailing end of a sheet are carried out. Also, in the apparatus, it is not detected at the early stage that a sheet jam has occurred in the neighborhood of the pressing plate, that the pressing plate is not actuated for any reason or that the pressing plate can not properly operate on a sheet because the sheet is severely curled. Especially, if a sheet jam is not detected at the early stage, the successive sheets are coming one after another, thereby wasting many sheets, bringing an abnormal load on the pressing plate and damaging the drive mechanism.
Furthermore, with a mechanism that refeeding means is pressed by the pressing plate via sheets, the drive mechanism of the pressing plate is given a load in proportion to the amount of the sheets in order to keep a travel of the pressing plate constant. Accordingly, there are problems that the more amount of sheets that are stacked, the larger the load the drive mechanism is given, and that the pressure to feed the sheets is varied in accordance with the amount of the sheets.